This is really old one.
The CIA was recruiting for a top secret assignment. They were
down to three recruits, two men and one woman. Only one could
get the position. As a final test each recruit was led down a
hallway to a large gray door. The CIA agents say to the first
man, "We need to know that you will do whatever we say
regardless of the circumstances. Take this gun, go into this
room and kill your wife". A look of shock comes over the man's
face. He says, "I can't kill my wife. I just can't do it. I
guess I'm not the man for this job". "No, you're not", agree
the agents, "You're free to go".
They bring the second man to the door and say, "We need to know
that you will do whatever we say regardless of the circumstances.
Take this gun, go into this room and kill your wife". The man
takes the gun and goes into the room. The room is silent and
after five minutes the man opens the door, tears streaming down
his face. "I tried," he says, "but I just couldn't do it. I can't
kill my wife". The agents let him leave.
They bring the woman to the door and say, "We need to know that
you will do whatever we say regardless of the circumstances. Take
this gun, go into this room and kill your husband". She takes the
gun and before the door closes behind her, she shoots off all 13
rounds emptying the gun. The door closes behind her and for the
next five minutes the agents hear loud banging and grunting. The
door finally opens, revealing the sweat-drenched woman. She looks
at both agents, wipes her brow and says, "Whew! You guys didn't
tell me that the gun was filled with blanks - I had to beat him to
death with the chair!"